The present invention relates to a collimator control method and an X-ray CT (Computed Tomography) apparatus, and more specifically to a collimator control method for an X-ray CT apparatus, which helically scans a subject with an X-ray beam formed by a collimator, and an X-ray CT apparatus which performs collimator control.
When a helical scan is performed, an X-ray tube and an X-ray detector are rotated around a subject to be photographed and a table with the subject placed thereon is linearly moved. A multi-row detector or a plane X-ray detector is used as the X-ray detector and an X-ray beam is formed as a cone beam in association with it, so that the efficiency of acquisition of X-ray data through the helical scan is improved. A collimator for forming the X-ray beam as the cone beam has an aperture width held constant during the helical scan (refer to, for example, the following patent document 1).
[Patent Document 1] Japanese Unexamined Patent Publication No. 2003-052684 (Fifth page and FIG. 5)
Since X-ray data unused in image reconstruction are also acquired or collected at start and end points of the helical scan in the above X-ray CT apparatus, the irradiation of X rays corresponding thereto results in needless irradiation. Thus, the X-ray irradiation is not preferable in view of exposure of a patient.